According to an article in my newspaper yesterday, the Red Bull had floor problems already a lot the end of last year, causing a disconnect between front and rear behaviour. That's gradually become worse through their upgrades (well, downgrades) over the course of this year.
Previously, that affected Pérez much more than Verstappen, since Verstappen was better able to work with it and get top performances anyway. But it's by now come to a point where he can't compensate anymore either, which supposedly explains why their performances aren't as far apart anymore.
Apparently, the Red Bull floor is super complex, much more than other teams. And they also have a year or cumulative upgrades to consider to find where they went wrong. So there's no easy fix, it's difficult to pinpoint the exact issue.
I was thinking that leads to two takeaways. One, Verstappen has a decent chance of suddenly getting his car back. It's not a certainty by a stretch, but there's a lot of potential in the car that can be unlocked by the right fix, probably more than for anyone else. If that happens, Norris's current advantage might be largely gone again.
And second, maybe Newey got this wrong as well. He's been gone for a while of course, but if the problems really did start last year, then he was still part of the team when they started going down the wrong path. It's obviously impossible to actually know who's responsible for what exactly, though.